Certain aspects of protein synthesis will be investigated. Translation by ribosomes of natural polycistronic mRNA will be studied with purified polysomes free of initiation factors. Polypeptide formed from these polysomes will be identified with specific antibodies made against it. N-terminal amino acid, the size and relative amount of the peptides formed will be analyzed and the results should enable us to determine whether ribosomes come off at the end of a gene or at the end of a mRNA. The role of a ribosome release factor in this process will be analyzed. The mechanism of ribosome release by this factor and its possible role in regulation of protein synthesis will be studied with purified factor from bacteria as well as from eukaryotic cells. A general search for conditional lethal mutants in translation, altered in components of interest, will be initiated. These studies should advance our knowledge of how a functional protein or a hereditarily defective protein is synthesized and controlled. The selective action of several antibiotics on protein synthesis will be further analyzed. Having found that spectinomycin and erythromycin, like streptomycin, block initiating ribosomes at some step after initiation, we plan to identify the blocked step for each and possibly to extend this approach to additional antibiotics. The mode of action of the aminoglycosides, gentamicin and streptomycin will be differentiated. These studies should advance our knowledge of the complex function of the ribosome and should help lay the ground work for future studies of conformational differences between ribosomes blocked in different states by different antibiotics.